1. Field of the Invention
The present invention relates generally to a device that can be installed in the reactor vessel of a boiling water reactor (BWR) to maintain the proper gap between the jet pumps and the riser brackets installed within the riser region of the BWR reactor vessel. More particularly the invention relates to a device that can easily replace existing jet pump jack screws and/or restrain jack screws that have loosened.
2. Description of Related Art
Boiling-water reactors (BWRs) are used for direct-cycle type power production. In other words, the reactor and steam plant are essentially one and the same. Thus, there is no separate primary coolant system and secondary steam plant system.
FIG. 1 depicts the elementary features of a conventional BWR plant. In the BWR plant 10, the reactor coolant is converted to steam within the reactor vessel 12, the steam is then directed to turbine generators 14, is condensed, and fed back to the reactor vessel as feed water. The feed water enters the reactor vessel and has its flow adjusted through the core by the recirculation system.
The recirculation system 20 of a BWR plant, depicted more specifically in FIG. 2, comprises recirculation pumps 22, jet pumps 24, and interconnecting piping 26 and valves 28. Feed water enters the reactor vessel annulus 32, located between the reactor vessel 12 and the core shroud 13. The feed water flows down the annulus 32, upward through the core region 34 and exits as steam. The circulation through the core is maintained by the recirculation system 20. This recirculated water is directed via the recirculation pumps 22, at high pressure and velocity, to the jet pumps 24, which enhances the total flow of feed water through the jet pumps 24.
A typical jet pump installation arrangement is shown in FIGS. 3 through 5. In the depicted arrangement, two jet pumps 24 are installed in the reactor vessel annulus 32. The jet pumps comprise an inlet 21, a mixer 23, and a diffuser 25. The jet pumps are aligned and laterally supported by a restrainer 27 that is connected to a riser 29. The riser 29 receives the incoming flow from the recirculation pumps 22 and directs the flow to the jet pump inlets 21. As shown more particularly in FIGS. 4 and 5, the jet pumps are held in vertical alignment by a riser bracket 31. The riser bracket 31 physically abuts the riser 29 and encompasses the jet pumps 24 in the pump mixer region 23. Lateral restraint within the riser bracket 31 is maintained by a wedge 33, and a plurality of jackscrews 35 positioned around the periphery of the jet pumps 24.
The recirculation pumps 22 and jet pumps 24 control coolant flow rate through the BWR core region 34. Moreover, as a result of the negative reactivity feedback mechanism of the coolant (e.g., void feedback), these pumps can affect core power level and power distribution in the core. Thus, it is important that the jet pumps 24 operate optimally. This in turn requires that the jet pumps 24 be maintained in vertical alignment. This vertical alignment, as noted above, is in part provided by the jackscrews 35 positioned around the periphery of the jet pumps 24. When the jet pumps 24 are installed and aligned, the jackscrews are adjusted and then welded in place. During operation, however, a gap can develop between a jet pump 24 and one or more jackscrews, due to operational vibrations. Typically, the maximum tolerable gap is on the order of 0.01 inches, and if this gap tolerance is exceeded, the welds must be broken and the jackscrews replaced. This type of repair is both time-consuming and costly. Additionally, the jackscrew welds may be broken, allowing the jackscrews to become loosened and fall into the reactor vessel. If broken welds are discovered during an outage, repair must be effected.
Hence, there is a need in the art for a device that can provide lateral support for BWR jet pumps to maintain their vertical alignment, without effecting costly repairs. There is also a need for a device that can restrain existing jackscrews whose welds have broken, thereby preventing them from falling out.
It is therefore a principal object of the present invention to provide a jacking device that maintains the proper vertical alignment of BWR jet pumps, when the gap between the jet pump and existing jackscrews is too large.
It is another object of the present invention to provide a clamping device, used in combination with the jacking device, that restrains existing jackscrews whose welds may become broken due to the effects of operational vibrations.
It is yet another object of the present invention to provide a method for installing the above-described devices in the vessel of a BWR.
In one aspect of the present invention, a jacking device includes first, second, and third members, and a jacking screw. The first and second members have sloping side portions. The third member has a plurality of sloped side portions and a threaded opening extending from its top portion through to its bottom portion. The third member is movably supported between the first and second members. The jacking screw engages the threaded opening in the third member.
In another aspect of the present invention, a jacking device for use with a BWR jet pump includes first and second jack blocks, a wedge piece, and a jacking screw. The jack blocks each include sloping side portions having a slot extending in the direction of the slope, and a dual-chamfered side portion positioned opposite the sloping side portion. The wedge piece is positioned between the sloping side portions of jack blocks and includes a plurality of sloped side portions. These sloped side portions each include a slope coextensive with one of the sloping side portions and a projecting portion that engages one of the slots. The wedge piece also includes a threaded opening extending through it from top to bottom. The jackscrew engages the threaded opening.
In yet another aspect of the present invention, a jacking device for providing contact between a jet pump and a riser bracket includes first jacking means, second jacking means, wedge means, and adjustment means. The first jacking means contacts an outer surface of the jet pump, and is movable in a first direction. The second jacking means contacts a surface of the riser bracket, and is movable in a second direction, opposite to the first direction. The wedge means moves the first and second jacking means in the first and second lateral directions, and is positioned between the first and second jacking means and is movable in a third direction, perpendicular to both the first and second directions. The adjustment means moves the wedge means in the third direction.
In still another aspect of the present invention, a jacking device for use with a boiling water reactor jet pump and riser bracket includes first and second jack blocks, a wedge piece, a jacking screw, a washer, a clamp, and a clamp screw. The jack blocks each include sloping side portions having a slot extending in the direction of the slope, and a dual-chamfered side portions positioned opposite the sloping side portions. The wedge piece is positioned between the sloping side portions of the jack blocks and includes a plurality of sloped side portions. These sloped side portions each include a slope coextensive with one of the sloping side portions and a projecting portion that engages one of the slots. The wedge piece also includes a threaded opening extending through it from top to bottom. The jackscrew engages the threaded opening. The washer is supported on top portions of both jack blocks and has an opening through which the jackscrew extends. The clamp is supported on an end, proximate the dual-chamfered side, of one of the jack blocks. The clamping screw extends through a threaded opening in the clamp and into a clamp screw opening in one of the jack blocks.
In still a further object of the present invention, a method of providing lateral alignment between a BWR jet pump and a riser bracket includes the steps of positioning a jacking device between the jet pump and riser bracket, and rotating a jacking screw. The jacking device includes first and second blocks, and a third block positioned between them. The jacking screw is rotated into a threaded opening of the third block to thereby move it in a vertical direction. The third block""s vertical movement causes horizontal movement of the first and second blocks. The rotation of the jacking screw is continued until the horizontal movement brings the first and second blocks into contact with the jet pump and riser bracket.